Ozone is an allotropic form of oxygen containing three oxygen atoms in the molecule. Ozone is unstable. Its half-life in air is about twenty minutes. Inasmuch as ozone may not be stored, in order to be usefully employed, it must be generated on site. As to the production of ozone in useful quantities, it may be generated by exposing dry air, or oxygen, to ultraviolet light, or to a high voltage electric field that is corona discharging at the surface of the conductors.
Ozone, if dispersed in air, will oxidize any organic or inorganic impurities present in the air that are susceptible to being oxidized. If the impurity is an organic compound, and the oxidization process runs to completion, the impurity will be reduced to carbon dioxide and water. The propensity of ozone dispersed in air to oxidize impurities in the air has in the past been utilized for removing odoriferous impurities from air.
There are several advantages to using ozone to remove odors from air. The principal advantage is the simplicity of the process. All that is required is a closed chamber containing the air to be treated and an ozone generator. A second advantage involving the use of ozone is that there are no filters that must periodically be cleaned and replaced inasmuch as the process does not utilize filters. A third advantage is the end products of ozone purified air generally are carbon dioxide and water, which are both harmless substances.
There are, however, several disadvantages to using ozone to remove odors from air. The principal disadvantages are that for airborne ozone to be an effective odor control agent, the ozone must be present in the air to be treated at a concentration of about 10 to 20 parts per million (volume), and the ozone must be approximately evenly dispersed throughout the air. Furthermore, the ozone concentration must be maintained until the odoriferous compounds in the air have been oxidized.
The length of time required to remove all odor from a volume of air will necessarily depend on the ozone concentration, the concentration of the odoriferous compounds in the air, and the nature of the compounds. The higher the ozone concentration in the air to be treated, the faster odors will be removed from the air. Continuous efforts are required, however, to maintain a desired concentration of ozone in the air, because ozone's half-life in air is about twenty minutes. The output of an ozone generator may be directed into a chamber containing air, but because half the ozone in the chamber will break down into molecular oxygen (O.sub.2) in about twenty minutes, the maximum amount of ozone that can be achieved in the chamber will be approximately one-half the amount of ozone made by the ozone generator during the period of one hour.
To obtain a desired concentration of ozone in the chamber, the chamber must be of such size that the amount of ozone generated by the ozone generator during half an hour, when mathematically divided by the amount of air in the chamber, equals the desired ozone concentration. If the chamber containing the air to be purified is large compared to the output of the ozone generator, the ozone concentration in the chamber will remain low, regardless of how long ozone is directed into the chamber from an ozone generator.
Other disadvantages to using airborne ozone to remove odoriferous compounds from air are associated with the fact that an ozone concentration that is sufficiently high to remove odors from air within a reasonable period of time is not safe for breathing. The Environmental Protection Agency has established an airborne ozone concentration of 0.5 parts per million (volume) as the safe upper limit for breathable air.
Another disadvantage to using airborne ozone to remove odoriferous compounds from air involves a time factor, for several minutes to an hour or more of reaction time is typically required for the desired result to be achieved. The required reaction time will depend on the ozone concentration and the nature of the odorous compounds in the air. Also, a "cooling down" period may have to follow the reaction period, during which the ozone concentration is allowed to decay to less than 0.5 parts per million, so as to below the safe upper limit for breathable air.
Still another disadvantage to using airborne ozone to remove odoriferous compounds from air is that a batch type process rather than a continuous flow of air process is involved, thus limiting this procedure to tasks such as deodorizing a room that may be sealed for a few hours, or for use in a confined area where humans normally would not be present, such as the lift chamber of a sanitary sewer lift station.
Ozone is soluble in water. Ozone reacts with water to form hydrogen trioxide (HO.sub.3) and hydroxide (OH), which in turn react to form hydrogen dioxide (HO.sub.2). Both hydrogen dioxide and hydroxide are strong oxidizers. They each react with many impurities, including microorganisms, such as bacteria and virus, destroying the impurity by oxidizing it. The possible achievement of these advantages readily explains why ozone is now commonly injected into municipal water supplies as a purifier and disinfectant.
If ozone is dissolved into water and the resulting mixture is sprayed into air as a fine aqueous mist, the ozone/water combination will almost immediately remove all odors from the air. The process is synergistic. Dissolving a given amount of ozone into water and then spraying the ozone containing water into a given amount of air will remove odors from the air many times faster than spraying pure water into the air or flowing the same amount of ozone directly into the same amount of air. The reaction is very fast because the ozone dissolved into the water reacts with the water to form hydrogen dioxide and hydroxide. Hydrogen dioxide and hydroxide, both of which are oxidizers, react very fast at the surface of the water spray's water droplets with any impurities in the air.
It is important to understand that spraying water containing dissolved ozone into air as very fine droplets as a means for removing impurities in the air has some major advantages over simply flowing ozone into the air to be purified. The reaction between the spray and any impurities in the air is very quick. The odor removal process may, for example, be carried out in a duct carrying a continuous flow of air to be purified. Also, because ozone, upon dissolving into water, reacts quickly with the water to form hydrogen trioxide and hydroxide, which in turn react to form hydrogen dioxide, there is little ozone remaining in the water to bubble out of the spray. This serves to alleviate concerns that the treated air might be a health hazard because of it containing in excess of 0.5 parts per million of ozone.
In order to be able to spray fine droplets of water containing ozone into the air in order to remove impurities from the air, it is necessary to first cause ozone to be absorbed in proper quantities into the water to be sprayed. Ozone can be dissolved into water by bringing gaseous ozone into contact with the water. The speed with which a given quantity of gaseous ozone will be absorbed by water depends on several factors, one being the size of the contact surface between the gaseous ozone and the water. The greater the contact area, the greater the speed at which the ozone is absorbed by the water.
A fine spray of liquid has a very large surface area for the volume of liquid contained in the spray. Ozone may be quickly dissolved into water by spraying a fine spray of water into an atmosphere containing ozone. The total surface area of the fine water droplets increases as the size of the water droplets decreases. Ozone in an atmosphere into which fine water droplets are being sprayed will be removed from the atmosphere and dissolved into the water droplets very quickly if the water droplets are very small and there is churning contact between the atmosphere and the water droplets.
The pneumatic atomizers of Erb and Resch, U.S. Pat. No. 3,993,246; Erb and Resch, U.S. Pat. No. 4,018,387; Erb and Resch, U.S. Pat. No. 4,161,281; Erb and Resch, U.S. Pat. No. 4,161,282; Erb and Resch, U.S. Pat. No. 4,261,511; Erb and Resch, U.S. Pat. 5,232,164 and Erb and Resch, U.S. Pat. No. 5,337,962 all involve elements that produce a thin liquid filaments or thin liquid ribbons and introduce the thin ribbons or filaments to an adjacent high speed flow of propellant gas. The thin ribbons or filaments of liquid are entrained into the flowing gas as thin ribbons or filaments of liquid, that are drawn out into elongated ribbons and threads that break up into smaller ribbons and threads of liquid, that in turn are drawn out and elongated by the propellant gas and break up into even smaller ribbons and threads. The foregoing drawings out, elongating and breaking up of the threads and ribbons of liquid repeats and continues until the liquid is in very small threads, ribbons, and irregular particles, which very small threads, ribbons and irregular particles collapse into spherical droplets. All of the foregoing takes place in the above identified pneumatic atomizers slightly downstream in the flowing propellant gas from the location where the thin liquid ribbons or filaments of liquid are introduced to the propellant gas.
It is of course known that a spherical liquid droplet has a smaller surface area than the same volume of liquid in any other shape. For example, a drop of liquid in the form of a thread has greater surface area than the same drop has after the drop has collapsed into a spherical droplet. The liquid in the thin ribbons or filaments of liquid entrained in the propellant gas flowing out of the above identified pneumatic atomizers has its greatest surface-area-to-volume ratio where the small threads, and ribbons of liquid described above are breaking up into irregular particles, which irregular particles collapse into small spherical droplets. The place where that occurs in the above-identified pneumatic atomizers is slightly downstream in the flowing propellant gas from the location where the thin liquid ribbon or filament is introduced to the flowing gas. The fact that the greatest surface-area-to-volume ratio of the liquid being atomized occurs slightly downstream in the flowing propellant gas from where the thin liquid ribbon or filament is introduced to the flowing gas is important to the instant invention because gas absorption into a liquid can only occur on the surface of the liquid, and the greater the surface area of a given quantity of liquid, the faster the gas is absorbed into the liquid.
A thread of liquid or any other irregular shaped particle of liquid has areas, many areas, that curve more acutely than the curve of the surface of a spherical droplet containing the same volume of liquid. The parts of the surface of the liquid thread or irregular particle with such acute curves are unstable. The surface tension forces acting on the surface of the liquid in such areas and the internal pressure forces of the liquid in such areas are not balanced. This imbalance is the source of the force that causes a thread or irregular particle of liquid to collapse into a sphere. This is important to the subject invention because it appears that a gas, such as ozone, if introduced to the ribbons, threads or irregular particles of liquid that exist in the above-identified pneumatic atomizers just downstream from where the filament of liquid is introduced to the flowing propellant gas, will be rapidly absorbed into the ribbons, threads and irregular particles of liquid. This absorption will occur much faster than otherwise because of the aforementioned imbalance.
If the objective of the instant invention was simply to introduce ozone to water by means of a pneumatic atomizer with the intent that the water absorb ozone, and that the ozone-bearing water, in the form of fine droplets, be exposed to air to be decontaminated, the objective could have been achieved by using an already known pneumatic atomizer and causing the propellant gas to be a mixture of air and ozone. Such a method or device is not practical for introducing ozone into water by the use of a pneumatic atomizer inasmuch as ozone corrodes the surface of everything with which it comes into contact, excepting only very stable, non-reactive materials such as glass and certain stainless steels.
Thus it is to be seen that the highly corrosive nature of ozone makes it difficult to pressurize or propel ozone for use as the propellant gas in a conventional pneumatic atomizer, with it also being difficult to duct the ozone containing propellant gas to the pneumatic nozzle. Furthermore, a pneumatic nozzle used in this manner would need to be made from materials that ozone will not corrode, which of course represents a great challenge.
A second difficulty that prevents using a mixture of air and ozone as the propellant gas in known pneumatic atomizers is the ozone will be approximately evenly distributed throughout the propellant gas in such atomizers. Unfortunately, the region in the downstream propellant gas where the propellant gas breaks up the liquid into small droplets does not occupy the entire downstream flow of the propellant gas. Some of the propellant gas will bypass the region in which the liquid is being broken up into small droplets. The ozone in the propellant gas that bypasses the region where the liquid is being drawn out and broken into irregular particles will not be absorbed by the liquid. Not having been exposed to the liquid, this will result in undesired unabsorbed ozone downstream.
A third difficulty that prevents using a mixture of air and ozone as the propellant gas in known pneumatic atomizers is the propellant gas in many such atomizers exits the atomizer as an essentially smooth flow and is flowing as an essentially smooth flow where it breaks up the liquid into fine droplets. It is highly advantageous that there be turbulence in the propellant gas-ozone mixture where the propellant gas breaks up the liquid into small droplets because turbulence will cause the propellant gas-ozone mixture to come into churning contact with the small liquid droplets as they are being formed, resulting in the ozone in the propellant gas being in intimate contact with the liquid when the liquid is most receptive to absorbing the ozone.
The instant invention may be used to create fine droplets of water containing absorbed ozone being carried away from the device as a mist by a propellant gas that is essentially free of unabsorbed ozone, which mist may be directed into an atmosphere containing impurities in order that the impurities be removed.
The instant invention may also be used as an efficient means for mass transfer of ozone into water or other liquid by flowing water or the other liquid through the instant invention, and collecting the resulting fine droplets in a sump. An example of the foregoing use of the instant invention is the removal of metal ions from a solution by flowing the solution through instant invention, whereby the metal ions will be oxidized by the ozone absorbed into the solution as it passes through the invention. The resulting droplets are collected in a sump, and the oxidized metal ions are allowed to precipitate out of the solution.
The instant invention is particularly useful for removing what is commonly called sewer gas from air. Sewer gas is generated in sewer pipes by natural biological processes acting on domestic waste and reactions of industrial wastes. Sewer gas consists principally of hydrogen sulfide (H.sub.2 S) and organic and inorganic hydrocarbons. Sewer gas is naturally present at a sewer line's outlet, such as the receiving chamber of a waste water treatment plant or the receiving chamber of a waste water pumping station. If not controlled, the sewer gas will flow into the atmosphere, causing unpleasant odors downwind.
Waste water treatment systems currently in use control sewer gas by adding chemicals that prevent the occurrence of the natural processes that generate the sewer gas, such as Sodium Hydroxide (NaOH), to the waste water at or near the upstream end of a sewer line. This is necessarily expensive, because of the cost of the chemicals. Other known waste water treatment systems control sewer gas by using air scrubbers spraying solutions of chemicals. This procedure also is expensive because of the cost of the chemicals used in the solution, which must be constantly replenished.
In general, the waste water treatment industry has attempted to use ozone to control sewer gas, but without success because of limitations due to the short half-life of ozone, as discussed above, and because the industry has not in the past had an efficient, simple and low energy means for introducing ozone into water.
It was to overcome the manifest problems of the prior art that the various embodiments of the instant invention were evolved.